This invention relates to an apparatus and method for protecting underground cable from being damaged, and more particularly, to an apparatus and method for safeguarding underground fiber optic or other types of buried cables from impact or other physical damage during use.
Fiber optic cable is composed of a bundle of long, thin fibers of glass, plastic or other transparent material closed with a protective sheath. Encoded light pulses carrying audio and video signals are sent through the fiber much like electric current travels along a wire. The advantage for fiber optic cable over conventional cable lies in its transmission characteristics. Because of the fiber's thinness and superior attenuation characteristics, a fiber optic cable can carry a much higher rate of information over many more channels than a comparably sized wire cable.
Fiber optic cable is more difficult to lay than conventional cable. It lacks the tensional strength of conventional wire cable and will fracture at a much lower pulling tension. Furthermore, because of its construction, fiber optic cable is relatively inflexible. The fibers are generally bundled in a spiral fashion around a stiff steel support wire within a hard plastic protective sheath. Bending of the cable beyond a limited range can break the fibers within.
Because of the time and effort and cost require to lay underground cable, it is important that it be protected from damage in areas where suitable shading or fill materials are not available. Also, once the cable is laid, damage problems often arise in the buried cable areas when contractors need to backfill or perform other excavation activities. The use of plastic sheathing is often insufficient to guard the integrity of the underground cable resulting in substantial costly and time-consuming maintenance problems.
Typically, the cable laying process involves trenching or excavating a pathway 24" to 42" deep, laying polyethylene conduit to encase the cable, backfilling the trench, and then pulling the cable through the conduit. Approximately 5-10% of the mileage excavated involves rocky terrain, and these sections must be trenched using pneumatic impact hammers or rock saws. The problem occurs have back filling of the trench begins and large rock fragments weighing up to 250 pounds roll down onto the conduit, cut through its wall, and damage the cable inside. The polyethylene conduit has low impact and cut resistance and will not adequately protect the cable.
To remedy this problem, contractors have employed various methods to protect the conduit and cable. These are:
1. Hauling rock free fill dirt from remote locations in large tractor-trailer trucks. This dirt is laid over the conduit/cable in sufficient depths to protect it form the rocks during backfilling. This process is costly due to the distance dirt has to be hauled and its availability, Another problem with this method is the accessibility of the trench to haul trucks in mountainous or rugged terrain.
2. Utilizing concrete-type mixtures such as "sackcrete" which is dumped over the conduit/cable in sufficient depth to protect them from damage. The concrete material is activated by the moisture within the soil forming a hard barrier. These materials typically come in 50-80 pound bags, which must be carried by workers and individually dumped into the trench. This process is slow, costly, and exposes the workers to potential lifting type injuries. This also creates problems if the buried cable must be excavated for repair at a later date due to the concrete barrier that has formed over the cable/conduit.
Therefore, a need exists for an effective and efficient apparatus and method for protecting underground cable assemblies, particularly optical cable assemblies, in areas where suitable shading or fill materials are not available, which can be employed when contractors need to backfill or perform other excavation activities, and which can safeguard the integrity of the underground cable thereby avoiding substantial costly and time-consuming maintenance problems.